"You eat a sandwich."
Translation:Jij eet een boterham.
If you are from the Southern US, just translate "jullie" in your head as "y'all." Don't put that in the lesson, though. The -en verb ending is your clue that whatever is going on is y'all, and not you (one person). As far as je/jij, what I understand so far is that it has to do with emphasis. "Je" is the normal version without any special emphasis. "Jij" is used when you REALLY want to make a point about who is doing something. "YOU are eating the sandwich--I'm not." I've only been at this for a few days, so that may not be the best explanation, but it seems pretty close.